Mechanism of point-defect diffusion in a two-dimensional colloidal crystal

DaSilva, L. C.; Cândido, Ladir; Hai, Guo‐Qiang; Oliveira, Osvaldo N.

doi:10.1063/1.3615287

Cited by 5 publications

(9 citation statements)

References 13 publications

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“…These colloidal model systems allow manipulation of the kinetic states of individual particles by means of optical tweezers, for example to create vacancies and interstitials [14,15,16,17,18], or to manipulate many-particle defect reactions [19]. However, the response of colloidal crystals to large thermal and external excitations of a single particle within the lattice is largely unexplored.…”

Section: Introductionmentioning

confidence: 99%

Highly cooperative stress relaxation in two-dimensional soft colloidal crystals

Meer

Fokkink

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it is well established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal stresses. We investigate, both experimentally and in simulations, how highly localized stresses relax in 2D soft colloidal crystals. When a single particle is actively excited, by means of optical tweezing, a rich variety of highly collective stress relaxation mechanisms results. These relaxation processes manifest in the form of open strings of cooperatively moving particles through the motion of dissociated vacancy-interstitial pairs, and closed loops of mobile particles, which either result from cooperative rotations in transiently generated circular grain boundaries or through the closure of an open string by annihilation of a vacancy-interstitial pair. Surprisingly, we find that the same collective events occur in crystals that are excited by thermal fluctuations alone; a large thermal agitation inside the crystal lattice can trigger the irreversible displacements of hundreds of particles. Our results illustrate how local stresses can induce largescale cooperative dynamics in 2D soft colloidal crystals and shed light on the stabilization mechanisms in ultrasoft crystals.collective dynamics | colloids | crystals | defects | stress relaxation S tress relaxation in crystalline solids is governed by the formation and diffusion of defects in the crystal lattice. For small deformations, it is well known that relaxation occurs through the motion of sparse dislocations (1-5). However, it remains unclear how a crystalline solid copes with stresses that are generated well inside the crystal, either caused by external sources (6, 7) or by thermal excitations, which can become especially important in superheated states (8-12). Particle rearrangements that result from large internal perturbations must necessarily involve the motion of many of the constituent particles simultaneously. Often these collective dynamics are rare due to large activation barriers in the dense solid state. As a result, studying largescale collective dynamics inside crystalline solids is challenging. One may expect that sufficiently large fluctuations, which could drive collective rearrangements, may only appear when the elastic energy associated with a fluctuation becomes on the order of the thermal energy. In crystals formed from colloidal particles that interact through long-range repulsive interactions, low-density and ultrasoft solid states are experimentally accessible in which large thermal excitations can be easily observed using optical microscopy (13). These very weak solids may exhibit fragility, the phenomenon that weakly stable solids display a nonlinear response to even very small external perturbations. Understanding the microscopic mechanisms of stress relaxation in these marginally stable materials is of fundamental importance to under...

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Section: Introductionmentioning

confidence: 99%

Highly cooperative stress relaxation in two-dimensional soft colloidal crystals

Meer

Fokkink

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…6,23 Note that both vacancies and interstitials are known to have many distinct topological configurations with different symmetries. 6,23 Note that both vacancies and interstitials are known to have many distinct topological configurations with different symmetries.…”

Section: B Microscopic Mechanisms For Diffusion In Crystal and Hexatmentioning

confidence: 99%

Dynamical heterogeneities and defects in two-dimensional soft colloidal crystals

Meer

Sprakel

et al. 2015

Soft Matter

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In this paper we study a two-dimensional system of charged colloidal particles using Brownian dynamics simulations. We determine the phase diagram and investigate the dynamics of this system in the density regime where hexatic and solid phases are stable. We find that the dynamics in these phases is heterogeneous by means of the spontaneous formation and diffusion of highly mobile defects. We identify two key mechanisms associated with the areas of high mobility. The first mechanism involves the highly cooperative motion of a closed loop of particles which shift coherently along the loop until each particle has replaced the position of its predecessor in the chain. The second mechanism involves the spontaneous creation of vacancy-interstitial pairs which diffuse within the hexatic and solid phases. We further explore quantitatively the properties of the open-ended and closed rearrangement strings and find that in the crystal phase the string-size distribution can be approximately matched with a simple, random walk description of vacancies and interstitials on a lattice.

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“…The examination of the energetics of vacancies in L-J crystals suggested that a sufficiently deep valley in the curve of the interaction potential is essential to support intact vacancies [21,22]. In contrast, the integrity of vacancies was hardly observed in systems of purely repulsive particles where the n-point vacancies tend to collapse into various defect clusters [15,28,[33][34][35]. We therefore expect a distinct scenario of vacancy dynamics in L-J crystals.…”

Section: Introductionmentioning

confidence: 97%

“…The problem of how the vacancy dynamics depends on vacancy size and temperature is still unclear. In addition, it appears that the behavior of vacancies is very sensitive to the nature of the interaction potential through a survey of the energetics [21][22][23][24] and dynamics [25][26][27][28][29] of vacancies in two-dimensional crystals with the Yukawa potential [25,[27][28][29], Gaussian core [30], the repulsive 1/r 3 potential [23], the purely repulsive Weeks-Chandler-Andersen potential [20], and the Lennard-Jones potential [21,22]. The generic, formally simple Lennard-Jones (L-J) potential represents an important form of interaction that has been extensively used to model a large variety of chemical and physical bonds [31].…”

Section: Introductionmentioning

confidence: 99%

Dynamics of vacancies in two-dimensional Lennard-Jones crystals

Yao

Cruz

2014

Phys. Rev. E

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Vacancies represent an important class of crystallographic defects, and their behaviors can be strongly coupled with relevant material properties. In this work, we study the dynamics of generic n-point vacancies in two-dimensional Lennard-Jones crystals in several thermodynamic states. Simulations reveal the spectrum of distinct, size-dependent vacancy dynamics, including the nonmonotonously varying diffusive mobilities of one-, two- and three-point vacancies, and several healing routines of linear vacancies. Specifically, we numerically observe significantly faster diffusion of the two-point vacancy that can be attributed to its rotational degree of freedom. The high mobility of the two-point vacancies opens the possibility of doping two-point vacancies into atomic materials to enhance atomic migration. The rich physics of vacancies revealed in this study may have implications in the engineering of defects in extensive crystalline materials for desired properties.

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Mechanism of point-defect diffusion in a two-dimensional colloidal crystal

Cited by 5 publications

References 13 publications

Highly cooperative stress relaxation in two-dimensional soft colloidal crystals

Highly cooperative stress relaxation in two-dimensional soft colloidal crystals

Dynamical heterogeneities and defects in two-dimensional soft colloidal crystals

Dynamics of vacancies in two-dimensional Lennard-Jones crystals

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